The parents of a British protester arrested for unfurling a giant banner opposite Beijing's Olympic stadium have defended their son's right to demonstrate over the situation in Tibet.

Brian and Bettie Thom, from Muir of Ord, near Inverness, were waiting anxiously at home to hear whether British officials had been able to speak to their son, Iain.

"We knew he was going out to protest. He is passionate about the Tibetan human rights situation, he wanted to do this and we have fully supported him. We are behind him all the way.

"If you have got something that you are passionate about you had to say what is right and what is wrong."

Mr Thom, who works in the construction industry, added that his son visited Tibet last year and had Tibetan friends in Edinburgh.

He was concerned about his son's welfare, but was also hopeful that the Chinese authorities would deport him. He has received one text message from his son saying that he is in custody but is being treated well.

He added: "I have spoken to British officials but there has been no news so far because they have not been able to speak to Iain, but we are hoping things will be resolved quickly "The Chinese government said protesters would be deported, and this was a peaceful protest that did not harm anyone.

He graduated from Edinburgh University with a first class honours degree in environmental geo-science and has worked with Friends of the Earth Scotland for the past few years.

A colleague in Edinburgh said he had many Tibetan friends who were delighted that he had been so successful of publicising the plight of their country.

Clare Symonds, who employed him at FoE Scotland, added: "He is a very bright guy who knew what he was doing. He has been planning this for some time. His Tibetan friends are very proud of him because he is doing something that they cannot do.

"They have told me today that he is a remarkable friend. I am hoping his Western passport will protect him and that he will be home soon."

Mr Thom was among four protesters arrested as demonstrations flared in Beijing. Tibet, religious freedom and anti-abortion activists all evaded tight security to launch guerrilla raids against key Communist Party policies. The protests were timed to cause maximum embarrassment to China on the day the Olympic Torch was paraded around the host city.

They passed almost unnoticed by Beijing's residents, but were publicised around the world through journalists and others alerted by a series of covert emails, phone calls and text messages.

Mr Thom and an American, Phill Bartell, 34, performed the most daring protest, climbing lighting posts near the "Bird's Nest" stadium at around 5.30am and unfurling banners saying "One World One Dream Free Tibet" - a parody of the official Beijing Olympics slogan "One World One Dream". One also said "Free Tibet" in Chinese.

Mr Thom spoke to reporters from the top of the pole by telephone, saying he was a long-term activist on the Tibet issue.

"This is a really critical time for Tibet," he said. "The Olympic Games are being used as a propaganda tool by the Chinese government to whitewash their human rights record."

Mr Thom's parents Brian and Bettie, from Muir of Ord, near Inverness, were waiting anxiously at home yesterday to hear whether British officials had been able to speak to their son.

According to state media, police "rushed to the scene" to remove the protesters. But Students for a Free Tibet, which organised the climb, said the banners remained up for at least an hour. All four were detained, with the other two demonstrators being named as Lucy Fairbrother, 23, a Bristol University graduate from Cambridge now living in London, and Tirian Mink, 32, from Oregon.

A British embassy spokesman said consular officials were trying to get access to those held. District police in Beijing said they had no comment.

Standard procedure would be immediate deportation to Hong Kong, but the Chinese authorities have already warned that foreigners who protest illegally risk being given "administrative punishments" - fines or jail terms without trial.

The Beijing Olympic Committee criticised the protest, which came shortly before the Torch was paraded from the Forbidden City, through Tiananmen Square and around the city as a triumphal climax to its circumnavigation of the globe.

It was cheered all the way by crowds of Chinese waving the national flag.

In a separate "action", journalists were summoned to a hotel near the Workers' Stadium where two westerners were waiting to show a film taped by two Tibetans, who travelled round their homeland recording views on the Games.

But almost as soon as the showing began, hotel officials demanded access and requested those present leave immediately.

No police were visible, or tried to detain the activists as they left, though a number of plain clothes security officers seemed to be watching the hotel.

"I have invited you to see a movie that a friend asked me to show to you," one of the two, both unnamed, said. He said he regretted he was unable to do so, and added that he had a "weird feeling" about whether he would be arrested or not later on.

A spokesman for Students for a Free Tibet warned that there would be more demonstrations as the Games unfolded.

The most complex stunt was arranged by anonymous religious freedom protesters. Visitors to specific rooms in two four-star hotels in the centre of the city were greeted by the sight of life-size dolls splattered with red paint to represent blood.

Red slogans were also painted on the wall, saying: "Speak out for those who have no voice", "One World One Nightmare" and "Sign the ICCPR". The ICCPR is the International Convention on Civil and Political Rights, which the Chinese have in fact signed but not ratified.

There was also a list of imprisoned pastors from China's underground "house churches", which refuse to register with the state-backed protestant church, and other prisoners of conscience.

A website linked to the protest, which was password-protected, contains articles on persecution of a number of religious groups, including the Christian churches but also Falun Gong, a quasi-Buddhist sect fiercely repressed by Beijing. Eventually the hotel rooms were shut down to outsiders.

More briefly, three anti-abortion activists were briefly questioned and then released in Tiananmen Square after shouting slogans attacking China's one-child policy.

"End the brutality," they yelled. "To those who are forced to go through forced abortions and have no voice, we are your voice."

A separate controversy was brewing last night after China revoked a visa issued to an Olympic gold medal winner who has been a prominent campaigner against Beijing's support for Sudan.

Joey Cheek is a leading member of activist group Team Darfur, which has targeted China's friendship with the Sudanese government for action in advance of the Olympics. As such, it is unsurprising that the American would be unwelcome to the authorities in Beijing.

But as the reigning men's 500-metre speed-skating champion from the 2006 Winter Olympics in Turin, he would normally expect to be welcomed at all subsequent Games.

The White House said it would protest to the Chinese authorities. The Chinese government says it has a right to deny entrance to anyone it sees fit.